Gases Flashcards
What is gas pressure?
The force exerted by gas molecules colliding with the surface of objects; P = F/A (force/area).
What is a gas?
Atoms that are independent from another.
What are SI units?
Metric (by ten) units made up of kg (mass), m (distance) & s (time).
What is a Manometer?
A manometer is an instrument that measure the pressure of a gas sample in an enclosed environment.
How to measure pressure in a manometer?
The volume (V) of a liquid is related to the height (h) of the column and the cross-section area of the tube (A). Since P = F/A and F = m*g and m = dV and V = Ah, Pressure = d(distance)h(height)g(gravity)
What is height a direct measure of?
In a tube where you have the known height of a liquid, height is the direct measurement of gas pressure.
What is a fluid?
Anything that flows (liquid or gas), so Earth’s atmosphere is a liquid.
What happens the further away from Earth you get, and the further you go into the atmosphere?
The further up you go, the lower (less) pressure gets because there is less atmosphere present above you.
How does gravity affect the atmosphere?
Gravity is the only think keeping gas molecules down to Earth. So, gravity causes the atmosphere to press down on the Earth’s surface, creating atmospheric pressure.
Why does heat (mostly) increase the further you go up in the atmosphere?
Different exothermic reactions generate heat and are more prominent in the upper levels of the atmosphere.
Order of atmosphere
Trophosphere < stratosphere < mesosphere < thermosphere < exosphere
What is a barometer?
A barometer measures atmospheric pressure. The pressure of the atmosphere is equal to the pressure of the liquid column (height) at equilibrium.
Boyle’s Law
At constant n and T, P is inversely proportional to V. (As pressure increases, volume decreases & vice versa.)
Charles’ Law
At constant n and P, V is proportional to T. (As volume increases, temperature increases & vice versa.)
Avogadro’s Law
At constant P and T, V is proportional to n. (As volume increases, the number of moles increases & vice versa.)
Ideal Gas Law
PV = nRT (explained through Boyle, Charles and Avogadro’s Laws.) It is a condition or state described by a certain set of P, V, and T values.
What calculations can we do with the special properties of Boyle’s Law?
When we have constant moles and temperature, we can solve for the pressure and volume and vice versa. For instance, if we known the V, T, and P at one point in the atmosphere and the P and T at another point, we can calculate V by comparing and cross multiplying because the increase should be proportionate.
(P1V1)/T1 = (P2V2)/T2
How do gases mix, and why is this important?
Gases mix homogeneously, which means that even though we can calculate partial pressures with the Ideal Gas Law, they cannot be measured in a lab sense.
For an ideal gas, what is the partial pressure?
The partial pressure in an ideal gas in a mixture is the pressure the gas would exert if it was alone at the same T and V conditions. (Charles’ Law)
Why is the atmosphere composition not uniform?
Gravity preferentially attracts heavier molecules towards the Earth’s surface, and the mixing of molecules is slow at the boundaries between layers.
What are the volumes of idea gases proportional to?
The number of moles (Avogadro’s Law) at constant T and P.
What defines the reaction stoichiometry using Avogadro’s Law?
The volume of the gas.
What is a mole fraction (X)?
It is the ratio between the number of moles of a component and total number of moles in mixture.
How can we calculate a mole fraction?
X = n(compound)/n(total). Similarly, X = P(compound)/P(total). So, P(compound) = X(compound)P(total).
What are the assumptions of the Kinetic-Molecular Theory of Gases?
- Particles move randomly in straight lines. 2. No attractive forces or repulsive forces between particles. 3. Particles collide without energy exchange (elastic collisions), no friction. 4. The particle volume is negligible when compared to total volume of the gas sample. 5. Particle kinetic energy is proportional to the temperature.
What happens when we increase volume at constant temperature?
Increasing V at constant T increases the distance particles travel before colliding with a wall, decreasing the number of collisions. So, when volume increases, pressure decreases (Boyle’s Law)
What happens when we increase temperature at constant volume?
Increasing T at constant V increases the average particle speed which increases the number of collisions. So, temperature increases with pressure (Charles’ Law.)
What is the average kinetic energy for a monoatomic gas?
av. KE = 3/2 (RT)
When does the Ideal Gas Law NOT apply? Why?
It does not apply to real gases at LOW temperatures or HIGH pressures because at low temperatures, molecules are slower and attractive intermolecular forces decrease the magnitude of collisions with surfaces so the observed pressure is less than the ideal pressure. At high pressures, the volume of the gas molecules is not negligible, therefore the observed volume is greater than the ideal volume.
What corrects for the assumptions made in the ideal gas law?
The van der Waals Equation
What is the Van der Waals equation?
(P+ (a)(n^2/V^2)(V-nb)
What is the natural greenhouse effect?
CO2 in the atmosphere absorbs infrared radiation emitted by the earth, releasing heat gradually over time.
